1. High resolution X-ray diffraction data have been collected for an aspartyl protease from Rhizopus chinensis, a renin analog. Several renin inhibitors have been analyzed bound to this enzyme. 2. The X-ray diffraction analysis of tryptophan synthetase from Salmonella typhimurium has been commenced. X-ray data to 2.8 A for the protein and two heavy atom derivatives have been measured and a preliminary analysis made. 3. Data have been measured for beef heart creatine kinase and a preliminary structural investigation has been made. 4. Neutron diffraction investigations of insulin and pancreatic trypsin inhibitor have been completed. Differences between the two independent molecules in the asymmetric unit could be accounted for by crystal packing forces. The trypsin inhibitor structure has given amide proton exchange data in striking agreement with NMR results. An investigation of small molecule hydrate structures has been carried out in order to obtain information about the ordering of solvent that will be applicable to proteins.